President Donald Trump was recently briefed on the opioid crisis, and he offered the following advice afterward. The "best way to prevent drug addiction and overdose is to prevent people from abusing drugs in the first place. If they don't start, they won't have a problem ... So if we can keep them from going on - and maybe by talking to youth and telling them: 'No good, really bad for you in every way.' But if they don't start, it will never be a problem."

It's obvious Trump has no understanding of addiction or abuse. His words are reminiscent of Nancy Reagan's "Just say no" policy and drug education endeavors such as the DARE program. The evidence is clear that "Just say no" and DARE were and are naïve and ineffective.

So the message is don't start, but for those who do, the Trump administration has a second prong to their approach, which is the criminal justice system and punishment.

Attorney General Jeff Sessions announced earlier this month the requirement that federal prosecutors must charge drug offenders with the most severe offenses possible. Sessions' words in the speech send a clear message. "In recent years some of the government officials in our country I think have mistakenly sent mixed messages about the harmfulness of drugs ... We cannot capitulate intellectually or morally unto this kind of rampant drug abuse. We must create a culture that's hostile to drug abuse."

For the past 50 years, we have been waging a war on drugs that has relied nearly exclusively on supply control and tough punishment. It hasn't worked.

Despite the logic of limiting the availability of drugs and threatening and punishing those who are involved in the drug trade and using drugs, the report card for "tough on drug crime" is bleak. We have invested more than $1 trillion during the past 45 years on the war on drugs. There is essentially no evidence in support of the success of that effort. One would be hard pressed to find many with knowledge of the war on drugs who would claim it has worked.

Why has it failed?

The medical community declared nearly 70 years ago that drug and alcohol addiction and dependence are medical disorders. We can't punish diabetes or cancer away. Why do we think getting tough on addiction would work?

To complicate the landscape, approximately 40 percent of opioid-dependent individuals have depression, anxiety or bipolar disorder, and some have co-occurring psychiatric disorders. Post-traumatic stress disorder and personality disorders are also present, though less frequently. Punishment is not only ineffective, it often exacerbates these mental health disorders.

Punishment also does not deter those with substance-use disorders. Today, the vast majority of individuals who enter the U.S. criminal justice system have problems with drug addiction, dependence or abuse. The recidivism rate for those with such disorders is nearly 80 percent. The reason is simple - punishment does nothing to address drug abuse, dependence or addiction.

It's time to stop disregarding the scientific and clinical evidence. It's time to get realistic about how we should address the drug problem. The evidence is unequivocal - we cannot effectively control supply. There is simply too much money to be made. We should recalibrate drug policy by dramatically ramping up evidence-based strategies of demand reduction. The only way to reduce the incidence of substance-use disorders is effective treatment. Ideally, that should occur outside the confines of the justice system with community-based treatment. Those who end up in the justice system should be diverted to treatment, not simply locked up.

Drug abuse is a public-health problem. It is time we treat it that way.

William R. Kelly is a professor of sociology at The University of Texas at Austin. His most recent books on criminal justice reform are "Criminal Justice at the Crossroads: Transforming Crime and Punishment" (2015), "The Future of Crime and Punishment: Smart Policies for Reducing Crime and Saving Money" (2016) and "From Retribution to Public Safety: Disruptive Innovation of American Criminal Justice" (2017).